1. Field of the Invention
This invention pertains generally to communication systems and, more particularly, to such systems providing communications to or from one or more electrical switching apparatus, such as circuit breakers.
2. Background Information
An electrical distribution system typically consists of a plurality of protective, metering and control devices mounted within an enclosure, such as a switchgear or motor control center metal cabinet or suitable plastic enclosure. A wired communication mechanism is often provided that allows the various devices to communicate with a display device on the enclosure or to communicate to a remote location, which monitors the condition of the system. The wired communication mechanism within the enclosure typically employs one or more wired field busses.
Electrical distribution devices, such as circuit breakers, are installed within the metal switchgear cabinet. Many of these devices are capable of communicating, for example, on-line data, and alarm/status, cause-of-trip and setpoint information. Typically, the wired field busses are “twisted pair” busses that interconnect the devices to a single node associated with the switchgear cabinet. There are numerous versions of that node including: (1) local nodes with a human machine interface (HMI) (e.g., displays and switches) intended for use on the cabinet; (2) nodes that are “headless” and serve as interfaces or gateways for connecting the devices to one or more remote communication systems; and (3) nodes that serve both the local and remote functions.
For example, an electrical distribution system may include a twisted-pair field bus network and a “headless” node that interfaces plural in-gear field bus communicating devices to an external Ethernet communicating system.
In terms of the health of the one or more electrical switching apparatus of an electrical distribution system, of particular interest are the conditions of the separable contacts and the temperatures of a bus bar or cable termination of an electrical switching apparatus, such as, for example and without limitation, a circuit breaker or contactor. For example, every time a circuit breaker or contactor interrupts a current, a certain amount of contact wear and erosion occurs. As the contact condition degrades, the contact resistance can result in a higher than normal contact temperature, which can compromise the insulation system. A higher than normal apparatus-to-bus bar or cable termination resistance can also result in an over-temperature insulation condition.
It is known to sense contact wear by noting the change in location of the moving contact from a fixed reference when a circuit breaker is in the closed position. As the contacts wear, this travel will increase. For example, U.S. Pat. No. 6,150,625 discloses an erosion gauge tool, which clearly provides an indication of the level of wear of separable contacts housed in a vacuum chamber. Also, U.S. Pat. No. 6,002,560 discloses a flexible, resilient contact wear indicator.
It is also known to directly assess the effect of a relatively high breaker-to-bus bar or cable termination resistance by measuring the bus bar or cable termination temperature. Breaker contact wear can also contribute to the termination temperature rise.
There is room for improvement in communications in electrical distribution systems and within or among one or more electrical switching apparatus.